support prometheus metric collection

[douglarek]

Please support Prometheus metric collection:

   serviceMonitor:                                                                                                                                                                                                                  
     enabled: true                                                                                                                                                                                                                  
     selector:                                                                                                                                                                                                                      
       release: prometheus                                                                                                                                                                            
     labels:                                                                                                                                                                                                                        
       app: rustfs